What I've read is that it makes errors happen more and maybe effect on control.
I haven't really tracked it (don't really get a ton of rain games, and don't "code" weather when I track stats), but the ones I've had seemed to play "differently" - that's about how I can describe it. Not necessarily causation, but rain games always seem to play somewhat differently than usual.
No objective data, so I won't say anything further than that. Just some possible observations.